Author Topic: Carbon fibre rod can it be cut down and used?  (Read 10007 times)

Offline bry1975

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Carbon fibre rod can it be cut down and used?
« on: July 29, 2011, 05:40:18 PM »
Chaps,

Solid carbon fibre rod can it be cut down and used without any  problems like fraying?

Offline Spurry

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Re: Carbon fibre rod can it be cut down and used?
« Reply #1 on: July 29, 2011, 06:40:42 PM »
Is that "cut-down" as in reduce diameter, or as in make a long piece shorter?

Pete

Offline bry1975

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Re: Carbon fibre rod can it be cut down and used?
« Reply #2 on: July 30, 2011, 08:04:59 AM »
Cut down the length the diameter will be kept at 2mm.

Offline Brass_Machine

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Re: Carbon fibre rod can it be cut down and used?
« Reply #3 on: July 30, 2011, 12:35:08 PM »
Yes it can. I do it all the time.

Wrap where you are going to cut in masking tape and cut with an abrasive cutting wheel. I use a chop saw with an abrasive cutting wheel but a Dremel with a cutoff wheel works too.

This is part of a cutting carbon tube FAQ:

Quote
CUTTING FAQ

How do I cut carbon fiber tubes? This is a common question and the answer will depend on what the type of cutting equipment you have access to and the amount of cutting you have. The tools required to cut carbon tubing could be as basic as a hacksaw or as extravagant as an industrial wet saw costing thousands of dollars. Before I get into the specifics of the task at hand let me remind you that Ultra Carbon Fiber (cfts) accepts no responsibility for injury or loss as a result of cutting carbon tubing. This FAQ is to be used as guide but you are solely responsible for the safe operation of any tools or equipment you decide to use. Working with power tools is dangerous and all possible safety measures should be taken to avoid personal injury. Now that we have that stuff out of the way let's move into he possible cutting options available. At the inexpensive end you can cut carbon tubing with a basic hacksaw. To cut tubing with a hacksaw I suggest wrapping the cut zone with a wrap or two of basic masking tape prior to cutting the tube. This will minimize fiber break out at the cut zone. In order to cut the tube you need to have a suitable way to hold the tube that is being cut. I would suggest a vice of the appropriate size for the tube and make sure the vice is equipped with rubber pads or some other padding to make sure you don't hurt the tube surface. Use very light clamping loads or you may delaminate a layer inside the tube. Use only enough pressure to hold the tube. Our stock tubes are designed to resist bending loads and not crushing loads. Although we can custom build custom tubes that will resist such loads you need to take great care when clamping our stock tubes. The relative strength and stiffness of a given tube depends mainly on fiber orientation so be careful. Once the tube is tape wrapped and clamped in place you can begin to saw the tube. Since you are using a hacksaw it would be a wise idea to cut the tube about 1/16" long and then sand back to your needed length. Saw in long smooth strokes and let the tool do the work. Carbon is very abrasive so don't expect a hacksaw to last more than a few cuts before it starts to dull. Use a hacksaw with very fine teeth like what you might use for cutting plastic or if you can find an abrasive only blade with no teeth that would be even better. Here is an example of a hacksaw blade with a carbide grit cutting edge:  I would not suggest a hacksaw for any type of production cutting but it would work for a few cuts. If you have an uneven cut you can block sand it square with 100-150 grit sand paper.

The second method for cutting tubing is similar to the first but instead of a hacksaw you can use a Dremel and a 7/8" diameter diamond coated cutting wheel. Here is a link to the cut off wheel as seen at Amazon: Dremel Wheel You can also purchase these wheels at your local hardware store Home Depot, Lowes etc but make sure you buy a Dremel brand wheel. Having tried knock off's from Harbor Freight and other sources they just don't math with the quality of a Dremel brand wheel. They aren't cheap at $15 but they make very precise cuts. The industrial diamond coating makes fast work of carbon and they last quite a long time. The main difference in cutting with a Dremel wheel and a hacksaw is one is powered and one is not. Since a Dremel spins at 15-30K rpm you will certainly need some safety glasses and a painters dust mask isn't a bad idea. A Dremel will kick off a lot of fine carbon dust which will cover everything around so keep that in mind when choosing a place to cut. You might also decide to have a helper hold a shop vac within about 5-6" of the tool to pull the dust while you make the cut. The dust is not toxic but the fine particles can get in your lungs so take the same precautions you would take when cutting wood for instance. The other downside to using a Dremel is that you can't make a square cut holding a tool free hand but you can black sand the cut end to square it up. Cutting the tubing at this rpm without a cooling medium (dry) not only kicks up dust but it heats up the resin in the matrix which will weaken the resin locally at the cut zone. In some applications this weakening may cause a structural issue but that will be left to your discretion.

Eric
Science is fun.

We're all mad here. I'm mad. You're mad.

Offline David Jupp

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Re: Carbon fibre rod can it be cut down and used?
« Reply #4 on: July 30, 2011, 01:39:20 PM »
The exact cutting detail can depend upon what the matrix is - epoxy or thermoset polyester perhaps most common, but if you have some rod with a thermoplastic matrix, don't try a high speed abrasive cutting technique!

Offline bry1975

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Re: Carbon fibre rod can it be cut down and used?
« Reply #5 on: July 30, 2011, 02:09:33 PM »
Thanks chaps,

Another question will carbon fibre rod scratch 316 SS?

It sounds a useful material and costs about 9.10 for FOUR metres of 2mm rod incl. postage!

TIA


Offline PekkaNF

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Re: Carbon fibre rod can it be cut down and used?
« Reply #6 on: July 30, 2011, 04:51:31 PM »
Hi. Since you probably will combine many materials, you may want to google "carbon fibre galvanic corrosion". Basics, aluminiums and low alloyed steels get cursory attention here: http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html

"will carbon fibre rod scratch 316 SS?" I have build few structures and wanted to but bearing to stainless/aluminium/carbon used teflon and POM. Pom is nicer to work with. I don't remember exact reason why I did avoid contact between carbon/stainless, could have been a word of senior engineer, my consideration to a sea water or over engineering.

Pekka

Offline bry1975

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Re: Carbon fibre rod can it be cut down and used?
« Reply #7 on: July 30, 2011, 05:14:49 PM »
Thanks for the link Pekka.

The Carbon fibre rods will be used with Hardwood so shouldn't be a problem as long as the material cuts well, has decent stiffness and is aesthetically pleasing.

Offline PekkaNF

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Re: Carbon fibre rod can it be cut down and used?
« Reply #8 on: July 31, 2011, 09:20:55 AM »
The Carbon fibre rods will be used with Hardwood so shouldn't be a problem as long as the material cuts well, has decent stiffness and is aesthetically pleasing.

Carbon fibre composites, even extruded rods, have pretty good stiffness. The problem when combined with the wood is that they are way more stiff than any wood. I.E. load sharing is done solely by carbon fibre when they are attached together. Learn that early when I tried to reinforce wing spars with carbon fibre. This is not necessarily problem if the structure is such that it does not bend, like knife handles, other member of the structure takes the forces.

Another consideration is fibre orientation, thin rods have fibres (and good strenght) only on longitudal direction. Twisting/crushing/splitting is not a good idea. Extruded pipes are pretty good on pull, very poor on twisting, because they have very low hoop strenght.

Epoxy works pretty good on freshly prepared carboncomposite/wood bonding. Mechanical fasteners are more of a problem (actually not a problem but need a little consideration) if they carry a load. You drill the hole and cut a bunch of fibres - you put a bolt trough it in the end of structure and load is carried completely by that small iasthmus right next to bolt. It does not work like a metal. Inserts and layers of cloth of different fibre orientation are used. Then again, if the member is more of a decorative than structural, good clean hole trough it would be fine. If trough screw needs to take user induced loads (good car dealership grin when torquing) or it's trough many structural members etc. an "insert" made of metal pipe or such to take up the compression will go long way. When I was a kid I saw one of my relative dive head first on clasfibre composites - apparently it was a steep learning curve for a self taught RR-bike mechanic.

Your projects are always interesting.

Pekka

Offline bry1975

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Re: Carbon fibre rod can it be cut down and used?
« Reply #9 on: July 31, 2011, 11:05:24 AM »
The idea is to replace the hardened pins below with Carbon fibre pins or a non ferrous metal, carbon fibre is cheaper to buy so will deffo try that.


Offline PekkaNF

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Re: Carbon fibre rod can it be cut down and used?
« Reply #10 on: July 31, 2011, 12:26:48 PM »
Intresting choice of materials.

Extruded carbon fibre rod has usually pretty low fibre concentration, thus might not bear close to theoretical loads (I'm not going into matrices here). They take pretty well load on their longitudal direction, but if they have to take shearing or twisting, particulary if machined to a shape those pins are on the picture I would predict them failing. I'm not specialist, but I have a little hands on experience on model aeroplanes. I does not "looks right" to my eyes.

Pekka

Offline bry1975

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Re: Carbon fibre rod can it be cut down and used?
« Reply #11 on: July 31, 2011, 01:07:14 PM »
Hi there,

The turning torque will be around 5Nm-15Nm maximum.
The pin protrusion is 3mm so basically stubbies.